Exposure controller for a camera
First Claim
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1. An exposure controller for a camera, comprising:
- a photometric assembly disposed within a camera which is adapted to effect TTL direct photometry, the photometric assembly including a first photoelectric transducer element designed for average photometry with emphasis on the central region of an image field and a second photoelectric transducer element designed for spotwise photometry, both transducer elements having light receiving areas disposed for photometry of light from an object being photographed which passes through a taking lens;
a photocurrent integrator for integrating an output current from at least one of the transducer elements;
a brightness difference decision circuit responsive to photometric outputs from the transducer elements to compare the brightness of a specific area on the image field against the brightness of its marginal area and to produce a brightness difference signal whenever the difference of the aforesaid brightness values assume a given relative value;
and an exposure correction circuit responsive to the brightness difference signal for altering the time when an exposure period is determined based on the comparison of an output voltage from the photocurrent integrator and a decision voltage preset in the camera, by a given amount in a direction toward overexposure.
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Abstract
An exposure controller for a camera effects a correction of exposure toward overexposure by automatically displacing the point in time when an exposure period is determined, whenever there occurs a difference in the brightness between a main subject to be taken and its background, which exceeds a given value, as a result of rear lighting or the like. In this manner, it is assured that the subject be photographed with a proper exposure.
53 Citations
14 Claims
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1. An exposure controller for a camera, comprising:
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a photometric assembly disposed within a camera which is adapted to effect TTL direct photometry, the photometric assembly including a first photoelectric transducer element designed for average photometry with emphasis on the central region of an image field and a second photoelectric transducer element designed for spotwise photometry, both transducer elements having light receiving areas disposed for photometry of light from an object being photographed which passes through a taking lens; a photocurrent integrator for integrating an output current from at least one of the transducer elements; a brightness difference decision circuit responsive to photometric outputs from the transducer elements to compare the brightness of a specific area on the image field against the brightness of its marginal area and to produce a brightness difference signal whenever the difference of the aforesaid brightness values assume a given relative value; and an exposure correction circuit responsive to the brightness difference signal for altering the time when an exposure period is determined based on the comparison of an output voltage from the photocurrent integrator and a decision voltage preset in the camera, by a given amount in a direction toward overexposure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A brightness difference decision circuit for use in an exposure controller circuit employed in a camera having a TTL direct photometry system comprising:
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a photometric assembly having a first photoelectric transducer element for providing average photometry with emphasis on the central region of an image field, and a second photoelectric transducer element for providing spotwise photometry, said first and second transducer elements having light receiving areas of different sizes disposed to receive light from an object being photographed and which passes through a taking lens; said areas A1 and A2 differing from one another by a factor K where A1 =KA2 and K>
1,amplifying means for amplifying the photocurrent produced by said second transducer element by a factor N to compensate for the difference in photocurrent magnitudes produced by the first and second transducer elements due to the difference in the light receiving areas of said first and second elements, and also to compensate for a difference in the photocurrent magnitudes produced by the first and second transducer elements due to a predetermined difference in the brightness of the light sensed by said first and second transducer elements; means for developing voltages from each of said photocurrents; and means for comparing said voltages for producing a brightness difference signal when the developed voltages differ by a predetermined value. - View Dependent Claims (13)
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14. A brightness difference decision circuit for use in an exposure controller circuit employed in a camera having a TTL direct photometry system comprising:
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a photometric assembly having a first photoelectric transducer element for providing average photometry with emphasis on the central region of a image field, and a second photoelectric transducer element for providing spotwise photometry, said first and second transducer elements having light receiving areas of different sizes diposed to receive light from an object being photographed and which passes through a taking lens; said areas A1 and A2 differing from one another by a factor K where A1 =KA2 and K<
1;means for altering the photocurrent produced by one of said first and second transducer elements so that the photocurrent produced by the transducer element having the smaller size light receiving area generates a photocurrent which is more than K times greater than the photocurrent produced by the transducer element having the larger size light receiving area to compensate for the difference in photocurrent due to the difference in size of the light receiving areas and also to compensate for a difference in the photocurrents produced by the first and second transducer elements due to a predetermined difference in the brightness of the light sensed by said first and second transducer elements; means for developing voltages from the photocurrents produced by said first and second transducer elements; and means for comparing said voltages for producing a brightness difference signal when the developed voltages differ by a predetermined value.
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Specification